Orbital stability and secular dynamics of the Proxima Centauri planetary system

The authors thank Gongjie Li, Hanno Rein, and Juliette Becker for valuable insights and discussion, and thank the anonymous referee whose thoughtful recommendations substantially improved this manuscript. This work was facilitated through the use of advanced computational, storage, and networking infrastructure provided by the Hyak supercomputer system and funded by the Student Technology Fund at the University of Washington.The two innermost planets of the Proxima Centauri system are separated by just 0.02 au, inducing strong gravitational interactions between them. We assess this interaction by leveraging fast orbital stability indicators and find that orbital stability is very likely if the initial eccentricities of planets b and d are less than ∼0.2, but cannot confirm stability at larger values. We find that stability is not strongly affected by the true masses of the planets or by the distant planet c. However, mutual inclinations between 95° and 142° often result in unstable motion. We further explore the long-term evolution of the orbits in these stable regions of parameter space and find that circularization can take over 5 Gyr. This tidal evolution could support surface energy fluxes in excess of 1 W m−2 for over 1 Gyr, possibly affecting planet b's habitability.J.R.L. gratefully acknowledges partial support from a Mary Gates Research Scholarship. R.B. acknowledges support from NASA grant No. 80NSSC20K0229 and the NASA Virtual Planetary Laboratory under grant No. 80NSSC18K0829.FacultyReviewe

2024 On the Verge Writing Contest Non-Fiction Honorary Mention

An award-winning work of non-fiction with the theme of equity, diversity, and human rights created by undergraduate student Ruby Harris, selected by celebrity judge Thembelihle (Thembie) Moyo.UndergraduateReviewe

Can there be a good scientific explanation that nobody understands?

My research looks at an ongoing debate in the philosophy of science about the nature of explanation. Central as data are three modes in which the term “explanation” is used: the representational mode, where models and theories explain phenomena; the ontic mode, where causes or mechanisms in the world explain phenomena; and the communicative mode, where people or groups explain phenomena to others. These different modes naturally employ diverging norms about how a successful explanation relates to the virtues of truth and understanding. For instance, in the communicative mode we often talk about explanations that simplify the facts to facilitate understanding. So we can see trade-offs where truth is sacrificed but understanding is gained. A mathematical model that is perfectly accurate but intractably complex would be an example of the opposite trade-off. Thus, puzzles arise over what is required for a putative explanation to really count as a scientific explanation. I researched philosophical arguments and surveys of opinion to familiarize myself with how philosophers and scientists view this complex relationship between explanation, truth, and understanding.Jamie Cassels Undergraduate Research Awards (JCURA)UndergraduateReviewe

Perceptions matter! Active physical recreation participation of children with high and low actual and perceived physical competence

Emerging evidence suggests that the accuracy of a child’s perceived physical competence (PPC) impacts participation in physical activity. We examined differences in active physical recreation (APR) participation based on clusters of high and low motor competence and perceptions from grades 3–5. Participants were a longitudinal sample (n = 155; 85 girls) of grade three, four, and five children. Fundamental motor skills (FMSs) were assessed using the TGMD-2, perceptions were assessed using the Self-Perception Profile for Children, and APR was measured using the Children’s Assessment of Participation and Enjoyment. K-means cluster analysis was used to create four clusters per grade based on participants’ FMSs and PPC z-scores. Differences in FMSs, PPC, and APR with cluster group as a factor were examined using a series of factorial ANOVAs. In each grade, participants in the high–high cluster participated in significantly more APR than those in the low–low cluster (p = 0.002 in grades three and four; p < 0.001 in grade five). Among the less accurate clusters (e.g., low FMSs with high PPC) was a trend toward positive FMSs growth among the children with higher perceptions. Results show that combinations of FMSs and PPC influence patterns of engagement or disengagement in active physical recreation persistently across middle childhood.This research was funded by an Insight Development Grant (2012–2014) (grant # 430-2012-0343) and an Insight Grant (2014–2017) (grant # 435-2014-1377) from the Social Sciences and Humanities Research Council of Canada.FacultyReviewe

Mapping vegetation height and identifying the northern forest limit across Canada using ICESat-2, Landsat time series and topographic data

The northern forest-tundra ecotone is one of the fastest warming regions of the globe. Models of vegetation change generally predict a northward advance of boreal forests and corresponding retreat of the tundra. Previous satellite remote sensing analyses in this region have focused on mapping vegetation greenness and tree cover derived from optical multi-spectral sensors. Changes in vegetation structure relating to height and biomass are less frequently investigated due to limited availability of lidar data over space and time in comparison with optical platforms. As such, there is an opportunity to combine lidar and optical remote sensing products for continuous mapping of vegetation structure at high-latitudes, with an emphasis on the forest-tundra transition. In this study, we used lidar data from the Ice, Cloud and land Elevation Satellite (ICESat-2) to classify canopy presence/absence, and predict canopy height across 120 million hectares of the Canadian forest-tundra ecotone at 30 m spatial resolution. Spatially continuous predictors derived from the Landsat satellite archive (2012−2021) and the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Digital Elevation Model were used to extrapolate 98th percentile canopy height from the ICESat-2 Land and Vegetation Height (ATL08) product using Random Forests models developed in R (version 4.2.2). Model accuracy was assessed using data from the Land, Vegetation and Ice Sensor (LVIS), a large-footprint airborne lidar system. The overall accuracy of the canopy presence classification was 89%, and canopy presence was detected with 88% accuracy. Models of vegetation height showed an overall R2 of 0.54 and RMSE of 2.09 m. Finally, we used these methods to map the limit of continuous 3 m forest across Canada and compared our model outputs with forest cover from the MODIS and Landsat Vegetation Continuous Fields datasets. This work demonstrates the challenges and potential for mapping horizontal and vertical vegetation structure within sparse, high latitude forests using both lidar and optical remote sensing data.This research was funded in part through the Canadian Space Agency (Grant number: 21SUESECDL) and by NSERC support of Nicholas Coops (RGPIN-2018-03851). We also acknowledge funding support to Hana Travers-Smith from the NSERC Canada Graduate Scholarship-Doctoral and the University of British Columbia.FacultyReviewe

Authigenic carbonate burial within the Late Devonian Western Canada Sedimentary basin and its impact on the global carbon cycle

Stable carbon isotope ratios (δ¹³C values) of marine carbonates are widely used to infer the relative burial rates of organic carbon, a source of oxygen to the ocean-atmosphere system. This inference, however, is based on the assumption that ocean-atmospheric carbon is buried either as organic carbon or as marine carbonate minerals. The burial of authigenic carbonate minerals formed within sediments after deposition, with low δ13C values (i.e., similar to organic carbon), has been proposed to explain high δ¹³C values in marine carbonates without the need for high burial fluxes of organic carbon. To test this hypothesis, we focus on the Late Devonian, a time period with both pervasive ocean anoxia and a severe reduction in shallow-water carbonate deposition—conditions hypothesized to promote authigenic carbonate formation. We present sedimentological and geochemical data from limestones and black shales of the Wabamun Group, Besa River and Exshaw formations of the Western Canada Sedimentary Basin. These data are compared to inorganic and organic weight percent measurements of North American shales acquired from the USGS National Geochemical Database (N = 4,437). Results show that basinal shale lack authigenic carbonate with low δ¹³C values and that the mean δ¹³C value of carbonate in these shales (−0.3‰) do not differ substantially from mean δ¹³C of carbonates in platform carbonates of a similar age (0.6‰). Furthermore, inorganic carbon content in Late Devonian shales (mean weight percent = 0.55%, N = 54) is lower than average Phanerozoic North American shale (mean of 1.95%, N = 4,055). Lastly, organic carbon-to-inorganic carbon ratios (OC:IC) of North American shales are well above 1 (mean = 3.72 for Late Devonian shales (N = 374), 2.25 for shales (N = 3,653) of all other ages). Therefore, even if the burial of fine-grained siliciclastic formations carrying authigenic carbonates were to increase, the concomitant increase in organic carbon burial would be even larger. Together, data from this study do not provide evidence that the burial of authigenic carbonate would have a significant effect on global carbon isotope mass balance.This research was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to J. Husson (RGPIN-2017-03887).FacultyReviewe

Turnover and the retention of Indigenous executives in Indigenous organizations

This dissertation explores the phenomenon of executive turnover within Indigenous organizations in Canada, addressing a critical gap in the literature on Indigenous leadership and governance. Drawing on mixed methods, including surveys, interviews, and focus groups with Indigenous executives and organizational leaders, the study examines the demographic and professional characteristics of Indigenous executives, the causes and impacts of turnover, and strategies for retention. It reveals that executive turnover is driven by factors such as lateral violence, burnout, inadequate compensation, and governance challenges, significantly affecting organizational stability and performance. Findings emphasize the importance of culturally grounded retention strategies, fair compensation, and improved governance practices to support Indigenous leadership. By identifying actionable insights and theoretical propositions, this work contributes to the development of effective policies and practices to strengthen Indigenous governance and self-determination.Graduat

It didn't affect me

An award-winning work of non-fiction with the theme of equity, diversity, and human rights created by undergraduate student Alex Da Matta, selected by celebrity judge Thembelihle (Thembie) Moyo.2024 On the Verge Writing Contest non-fiction honorary mentionUndergraduat

Arctic Politics in a Time of Change: A Study on the Impact of Deteriorating Relations on the Indigenous Peoples’ Inclusion in Arctic Decision-Making Processes

This thesis examines how the deterioration of Arctic politics since 2007, led by a changed geopolitical perception of the Arctic region and worsened relations between Russia and the West, has impacted the Indigenous Permanent Participants’ abilities to advance their own interests in Arctic governance. Through a textual analysis of research on Arctic politics and security, a discourse analysis of the Saami Council and the Inuit Circumpolar Council’s response to the Arctic Council’s suspension in 2022, and analysis of the Arctic Council’s structure and an examination of the Russian-West relations between 2007-2022, I argue that the deterioration in Arctic politics affects the Permanent Participants’ abilities to advance their interests in Arctic governance in two ways. First, it has increased state-centric decision-making in the Arctic Council, which largely leaves out the Permanent Participants from the Council’s decision-making processes. Second, it has increased the workload in the Council, which has heightened the Permanent Participants’ demand for funding in order to participate. I conclude that continued deterioration in Arctic relations will negatively affect Arctic Indigenous peoples, as they continue to remain constrained within their national contexts and other international institutions in regard to advancing their own priorities. Through the theoretical lens of securitization and ‘acts of indigeneity’, this study contributes to the understanding of how the Arctic Indigenous peoples strategically aim to situate themselves as political beings in the Arctic decision-making processes in response to the current deterioration in Arctic politics.Graduat

A Laboratory Study on the Influence of Guided Drop Tower Carriage Mass and Kinematic Differences to Full-Surrogate Free Falls Toward Enhanced Helmet Certification Methods

Falling from height presents a significant risk for military personnel due to the frequency at which they perform high exposure maneuvers, such as walking along unstable structures, repelling from buildings or aircrafts, and low altitude egressing. Traumatic brain injury (TBI) resulting from falls from height (FFH) account for approximately 20% of TBIs with a reported cause in the military, despite the presence of protective head gear. This is likely because current certification testing performed on military helmets emphasize protection against ballistic threats over blunt impacts, such as falls. Military personnel have identified the need for the next generation of helmets to provide better protection against blunt impacts. To develop such helmets, a method for helmet evaluation in scenarios that are representative of real-life falls must be established as the new standard for helmet impact testing. Guided vertical drop towers are a test device commonly used to evaluate the impact attenuating properties of protective headgear in headfirst falls during certification testing. These devices provide a simple, low cost, repeatable means for conducting certification tests over using full-body surrogates to replicate a person experiencing a headfirst fall. However, there are some limitations to the guided drop tower that may limit their ability to properly replicate a fall from height. The most notable limitations are that guided drop towers are constrained to only a single degree of freedom and the impact mass of a drop tower assembly typically only includes the mass of a human head and neck rather than the mass of a full-body. At present there is little work on how these limitations may yield a differing kinematic response between a guided drop tower and that of an actual fall. The objectives of this thesis was to determine if kinematic differences exist between a guided drop tower and a free-falling person, in unhelmeted and helmeted scenarios. The outcomes of this thesis will contribute toward the development of enhanced test standards that evaluate protective headgear in scenarios that are more representative of real-life falls. iii A custom guided drop tower equipped with a Hybrid III head/neck and adjustable weight drop carriage along with a full-body Hybrid III 50th percentile male surrogate, to represent a falling person, were subjected to two experimental series 1) unhelmeted impacts at four angles between 30° and 75° and four impact velocities between 1.50 m/s and 3.00 m/s and, 2) helmeted impacts at 30° and 75° with impact velocities of 3.00 m/s and 4.50m/s. Impacts in both series were conducted onto a rigid impact surface and kinematic measures of head center of gravity linear acceleration, angular acceleration, and angular velocity were measured. Results of the unhelmeted impact series identified that the drop tower can provide an acceptable approximation of the linear acceleration but not the angular velocity that is likely to be experienced by a person in a headfirst frontal impact. This is due to the angular velocity differing in either the magnitude of the peak angular velocity or direction and time instance of peak measures. Changes to the mass of the drop carriage, to be closer to that of a full dummy, did not bring angular velocity closer to that measured for the full dummy. The helmeted impact study identified that a drop tower is likely to yield an underestimate of peak kinematics in shallow angle impacts and an overestimate of peak kinematics in steep angle impacts. This suggests that the drop tower, in its current form, provides a varying estimate of the resultant peak kinematics in helmeted impacts which is dependent on impact angle. These differences in response are primarily attributable to variances in helmet liner engagement when comparing the drop tower and a person falling. The results of this research found that in their current form guided drop towers do not provide a true representation of the kinematic response that is likely to result in a headfirst fall, either unhelmeted or helmeted. Further the addition of mass to the drop carriage in either scenario did not alter the drop tower’s response to a point where it matched the measured response of the falling surrogate .These differences in kinematic responses between the drop tower and what is likely to be experienced by a falling person, specifically in the case of underestimated responses in shallow angle helmeted falls emphasizes the need to further develop testing methods to ensure that future helmets are evaluated in a way that effectively tests the helmet’s impact-attenuating abilities in an actual fall.Graduat